This invention relates to a vacuum operated servo, particularly to a vacuum operated servo using a diaphragm suitable for throttle positioning of a carburetor.
It is desirable that one vacuum operated servo can provide various positions because it has small space needed for its installation and its manufacture may bear a low cost. As this kind of servo, known is a servo used for throttle valve positioning which is described in Japanese Laying-open for Patent Application No. 51423/1974 and Japanese Patent Publication No. 35971/1975.
The servo has first and second chamber divided by a partition with an orifice, each of which chambers is provided a flexible diaphragms thereby to divide the chamber into two, vacuum and air chambers, so that the vacuum chamber of the first chamber will be in a back to back relation with the vacuum chamber of the second chamber. The diaphragms of the first and second chambers each have a plunger secured thereto at their central portions. The first plunger of the first chamber projects slidably through a hole made in the partition into the vacuum chamber of the first chamber, the second plunger of the secnd chamber projects out of the second chamber to contact with a throttle lever of a carburetor, which lever is mechanically connected to a throttle valve to control the opening of the throttle valve. The vacuum chamber of the first chamber communicates with an air-fuel induction passage downstream of the throttle valve, and further with the vacuum chamber of the second chamber through the orifice of the partition.
The servo provides three positions for the throttle valve, namely, a starting position, a curb idle position and antidieseling position through sliding movement of the plunger according to vacuum in the vacuum chambers.
A sliding portion in which the sliding movement is effected should be precisely finished, and sealed air-tightly. This realing for the sliding portion is difficult because it is necessary to seal without having any effect on the sliding movement. Further in the sealed sliding portion, the plunger which is slidably moved by the diaphragm has a danger such that the plunger may stick to the hole of the partition.
Therefore, desired is a servo for providing a plurality of positions without the above-mentioned sliding portion and sealing means of the sliding portion.